The present application generally relates to methods and systems for the non-intrusive determination of the chemistry of materials and mixtures. More particularly, the application relates to chemical assaying of hydrogenous materials and mixtures using combined neutron activation and nuclear resonance fluorescence.
The ability to determine the chemistry of bulk materials in a stand-off, non-destructive manner is valuable to many security and commercial operations in a global scenario. For instance, in the US, security operations such as Customs and Border Protection (CBP) and the Transportation Security Association (TSA) have a core mission to determine the presence of contraband in concealed containers. Additionally, commercial operations have interests for material tracking including applications such as supply chain control. Techniques for the detection and quantification of specified materials are valuable to these missions on a global basis.
Nuclear resonance fluorescence (NRF) (disclosed, e.g., in U.S. Pat. Nos. 5,420,905 and 5,115,459) is an established technique for the non-destructive determination of the presence of individual isotopes. Similarly, neutron capture by hydrogen provides a well-known gamma signal for its presence. However, many real-life situations do not allow the use of neutron beams to provide information concerning the hydrogenous content of a specific position in a container. This is generally due to attenuation of neutron beams by thick hydrogenous materials such as water or wood or other materials.
In chemical assaying techniques disclosed herein, the neutrons are generated within the sample itself, very near or at the location of interest within the container. Only the transmission of a photon beam is needed to reach a specific location, not the neutrons from an external beam. The techniques disclosed herein involve a novel method for neutron production and a fusion of the neutron capture signal with the signals from NRF. The result is a novel technique wherein during one common exposure by a photon beam, it is possible to discover and measure for a specific location in a container: (a) the hydrogenous nature of the material through neutron production from 2D(γ,n) and capture by hydrogen, (b) the presence of other nuclear species via the complimentary use of NRF, and (c) the nature of the hydrogenous chemical element or admixtures that are present in a specific location via the fusion of these data from (a) and (b).